y the inhabitants of one
region may be enabled from time to time to invade another, and do
actually so migrate and diffuse themselves over new countries. Now,
although our knowledge of the history of the animate creation dates from
so recent a period, that we can scarcely trace the advance or decline of
any animal or plant, except in those cases where the influence of man
has intervened; yet we can easily conceive what must happen when some
new colony of wild animals or plants enters a region for the first time,
and succeeds in establishing itself.

_Supposed effects of the first entrance of the polar bear into
Iceland._--Let us consider how great are the devastations committed at
certain periods by the Greenland bears, when they are drifted to the
shores of Iceland in considerable numbers on the ice. These periodical
invasions are formidable even to man; so that when the bears arrive, the
inhabitants collect together, and go in pursuit of them with
fire-arms--each native who slays one being rewarded by the King of
Denmark. The Danes of old, when they landed in their marauding
expeditions upon our coast, hardly excited more alarm, nor did our
islanders muster more promptly for the defence of their lives and
property against the common enemy, than the modern Icelanders against
these formidable brutes. It often happens, says Henderson, that the
natives are pursued by the bear when he has been long at sea, and when
his natural ferocity has been heightened by the keenness of hunger; if
unarmed, it is frequently by stratagem only that they make their
escape.[965]

Let us cast our thoughts back to the period when the first polar bears
reached Iceland, before it was colonized by the Norwegians in 874: we
may imagine the breaking up of an immense barrier of ice like that
which, in 1816 and the following year, disappeared from the east coast
of Greenland, which it had surrounded for four centuries. By the aid of
such means of transportation a great number of these quadrupeds might
effect a landing at the same time, and the havoc which they would make
among the species previously settled in the island would be terrific.
The deer, foxes, seals, and even birds, on which these animals sometimes
prey, would be soon thinned down.

But this would be a part only, and probably an insignificant portion, of
the aggregate amount of change brought about by the new invader. The
plants on which the deer fed, being less consumed in consequen